#[test]
fn main(){
    // Option
    let x = Some("air");
    assert_eq!(x.unwrap(), "air");
  }
  //编译通过

  #[test]
#[should_panic]
  
  fn main2(){
    // Option
    let x:Option<String> = None;
    assert_eq!(x.unwrap(), "air");
  }